1. Field of the Invention
This application relates generally to a method and apparatus for applying a multi-component coating of a desired composition over a substrate and, more particularly, to a method and apparatus for applying a multi-component refinish coating over an automotive substrate.
2. Technical Considerations
Automotive refinish coatings are used to cover damaged areas of a vehicle in order to restore the original appearance of the vehicle. Conventional refinish coatings are typically supplied to automotive repair shops in the form of multi-package systems. An example of one such system is a two-package system, with one package containing a polymeric material and the other package containing a catalyst or curing agent. When a refinish coating is to be applied onto an automotive substrate, the components in the separate packages are mixed together, typically at a particular ratio specified by the coating manufacturer, and the mixed coating composition is placed into a container. The container is connected to a coating device, such as a pneumatic spray gun, and the mixed coating composition is spray applied onto the automotive substrate.
While generally acceptable for most automotive refinish operations, this conventional refinish coating method does have some drawbacks. For instance, after mixing the separate components together, the pot-life of the resultant coating composition is typically limited to only about 30 minutes. By “pot-life” is meant the time within which the coating composition must be used before the coating composition becomes too viscous to be applied due to cross-linking or curing. Also, since most refinish coating jobs need only cover a relatively small area of a vehicle, the separate packages typically do not contain a large amount of the respective coating components. Therefore, for larger jobs, several different batches of the coating composition must be consecutively prepared and applied. This batch mixing increases the time required to coat a large substrate and requires the coating process to be intermittently stopped and started while batches of the coating composition are mixed. As will be appreciated by one skilled in the refinish coating art, it would be advantageous to increase the curing speed of the coating composition to decrease the curing time of the applied coating composition so that the applied coating could be more quickly sanded or further coatings applied. However, increasing the curing speed would also disadvantageously decrease the pot-life of the mixed coating composition.
In an attempt to alleviate some of these problems, spray devices have been developed in which specific amounts of the separate coating components are mechanically metered to the spray device to provide a desired coating composition. Examples of known coating dispensers are disclosed in U.S. Pat. Nos. 5,405,083; 4,881,821; 4,767,025; and 6,131,823. While generally acceptable, the mechanical pumping and metering equipment required to accurately meter specific amounts of the coating components to the spray device add to the overall cost of the system. Moreover, the metering equipment must be regularly checked and maintained to ensure that it is in proper working order to accurately supply the required amounts of the coating components to the spray device.
As will be appreciated by one skilled in the automotive refinish coating art, it would be advantageous to provide a method and/or apparatus for applying a multi-component coating onto a substrate which reduces or eliminates at least some of the drawbacks of known coating application systems.